Coastal dune topography as a determinant of abiotic conditions and biological community restoration in northern KwaZulu-Natal, South Africa

Abstract:

Topography is rarely considered as an independent
goal of restoration. However, topography determines
microenvironmental conditions and hence living
conditions for species. Restoring topography may therefore
be an important first step in ecological restoration. We
aimed at establishing the relative importance of topography
where coastal dunes destroyed by mining are rebuilt as part
of a rehabilitation program. We assessed the response of
(1) microclimatic and soil conditions, and (2) woody plant
and millipede species richness and density, to locationspecific
topographic profiles. We enumerated the topographic
profile using variables of dune morphology (aspect,
elevation, and gradient) as well as relative position on a
dune (crest, slope, and valley). Temperature, relative
humidity, and light intensity varied with aspect, elevation,
gradient, and position. However, regeneration age was a
better predictor of soil nutrient availability than these
topographic variables. Age also interacted with topographic
variables to explain tree canopy density and species
richness, as well as millipede species richness. The
density of keeled millipedes (forest specialists) was best
explained by topographic variables alone. The transient
nature of these new-growth coastal dune forests likely
masks topography-related effects on communities because
age-related succession (increasing structural complexity)
drives the establishment and persistence of biological
communities, not habitat conditions modulated by topography.
However, our study has shown that the microhabitats associated with topographic variability
influence specialist species more than generalists.